Fasting Two Days a Week Is Not a Bad Diet
Over the course of one day, I ate some green beans, a Clif bar, and one homemade sous vide egg bite . That’s 500 calories. I swear I don’t have an eating disorder – I just tried my diet. The next day, I went back to my normal 2,000 calories and felt great.
On a 5: 2 diet, let’s say you “fast” two days a week. Monday and Thursday. You eat 25 percent of your regular calories these days. On other days, you eat normally. By the end of the week, you had eaten the same number of calories as those suckers who received 1,500 calories, but you only had to spend two days on the diet.
This diet has been wildly popular in the UK for years, starting with a 2012 BBC documentary . When I first heard about it, I almost liked the idea. I used to stick to intermittent fasting, which basically boiled down to skipping breakfast and putting off lunch. It helps me focus better in the morning and seems to eat healthier overall, but it takes some getting used to.
Fasting all day sounded too difficult, but then again, it looks like half of England is doing it ( including Benedict Cumberbatch ). I needed to lose a few pounds and I get frustrated and hungry over traditional calorie-based diets, so I decided to try 5: 2.
Why would anyone do this?
It doesn’t matter that diet is the raison d’être of our existence , let’s be honest: most people are interested in losing weight. This is true here too. This diet, like other intermittent fasting diets, is also designed to improve your brain, heart, metabolism, and more .
The beauty is that you don’t have to stick to the 5: 2 diet for more than one day at a time. Sure, it’s a tough day, but it’s not at all like the Whole30 diet when you stick to a strict set of rules that ban bread and sugar for a month. And it’s not the endless tedious work of a typical calorie-added diet for long-term weight loss where you have to keep track of what you eat over the course of months or years .
The first day I tried to fast, by the end of the day I got hungry. To distract myself, I opened Facebook on my phone and my friends were sharing their favorite recipes for curry with fat coconut milk. I was seized by a fit of jealousy, but I thought, “Hey, I’ll do it tomorrow.” How many diets allow you to say this on the first day?
The 5: 2 diet itself has not been extensively studied, but there is some preliminary evidence. One long-term study found that a 5: 2 diet gave about the same results as a regular diet. Other studies of fasting every other day have shown similar results: according to studies like this one published in the journal Obesity , it helps you lose weight as well as traditional diets.
But it works better for some than for others, and researchers are trying to figure it out too. One study published in the journal Obesity Research and Clinical Practice found that whites and older adults are more successful in dieting, but there are many factors they overlook, such as whether certain groups have better access to healthy foods. Men and women are equally lucky with their diet.
Other health benefits besides weight loss are not easy to identify. We’ve known for a long time thatmice live longer when they are malnourished . There have been many studies trying to find out what other benefits of calorie restriction are , and whether they can be applied in humans in a safe and practical way.
For example, fasting should help your body learn to better control blood sugar levels. If you overeat, your cells can become insulin resistant, eventually leading to type II diabetes . Both diet and exercise seem to reverse this effect, and from what we know about how the body regulates blood sugar, fasting should help even more. Unfortunately, we don’t have enough evidence to tell if this is actually the case .
The book explaining the 5: 2 diet, The Fast Diet , is more honest about it than I expected it to be a diet book. Writer Michael Mosley , a physician-turned-BBC host, tried several fasting diets for his documentary Eat, Fast, and Live Longer . He explains that he settled on the 5: 2 pattern as a trade-off between different methods. Basically, this is based on his experience and intuition. I agree with it. We don’t have enough evidence to argue that fasting (or even dieting) should be done in a specific way, so if a 5: 2 ratio is acceptable and there’s a good chance of success, I think it’s worth a try.
What is a fasting day like?
I wake up thinking about breakfast. This is not excluded from the menu, but I only have 500 calories per day, and I would rather save them for later. So instead, I fill my stomach with some kind of drink: coffee, water, seltzer, diet cola. Cravings usually subside.
If this does not happen, I will go to have a snack with vegetables, since they are almost not high in calories . Trader Joe’s sells a microwave-safe bag of fresh green beans. With plenty of salt and pepper, it’s flavorful and almost filling, and the entire packet contains just 125 calories. I split this into morning and evening snacks.
Anyway, I’m usually fine by 2:00 pm. If I’m having trouble concentrating at work, then I know it’s time to eat. It can be a meticulously measured portion of just about any food, but I see no point in researching recipes, shopping, or preparing a snack. ( There are plenty of recipes for the fast diet , however, if that’s the approach you prefer.) The Clif bar is the one I go for the most: around 250 calories, depending on flavor. I find this to be as satisfying as you can expect from a 250-calorie meal.
I do not go until evening, and this is the most difficult thing for me. I wander through the kitchen, discussing how to spend the last 100 or 200 calories, making myself even more hungry. I love to eat something dense and satisfying, like an egg bite, but that never happens. Tomorrow I have to tell myself. I’ll have more tomorrow.
In fact, the easiest thing to do is not go to the kitchen and think about food. Fasting is easiest on days when I’m busy at work, and hardest on weekends, when I may have time to laze around or be at a party.
Can you exercise while fasting?
In short, yes, you can. I just planned my workouts and my hungry days so they don’t overlap. But one day I thought: why not try to go for a run and write about how awful it is.
It wasn’t scary. I was shocked: it was noon, and all day I did not eat anything except diet cola and seltzer water. I brought a Clif bar with me just in case, but ended up jogging for almost an hour without feeling hungrier than when I sat at my desk. I ran at my normal speed, and even ran longer than I originally planned. (Bad court-induced hunger? I’m not ruling out.) And then, I set Cliff’s bar aside and didn’t have a bite until the evening when I realized that I could treat myself to 400 calories of super burrites .
Some people say they have more energy when they exercise on an empty stomach . I always thought it was something to get used to , but I didn’t expect to experience it the first time. Maybe it was an accident. Maybe not.
What do you eat when you are not fasting?
On a fickle day, you need to eat “normally.” Nothing is taboo, but whether you are using it for weight loss or just living a healthy lifestyle, it would be wise to eat vegetables and protein rather than too many muffins.
I do get a little hungrier the day after fasting (although it’s easy to skip breakfast even if I was hungry before bed). But there is no guarantee that you will ultimately help out. “Reducing calories by 75 percent on a fasting day typically results in a little over 15 percent increase on the next day of feeding,” write Dr. Mosley and co-author Mimi Spencer in Fast Diet . They cite this study , which also noted that by the second week of fasting on fasting days, people feel less hungry. (Again, this study is about fasting every other day, not the 5: 2 diet.)
I found that I couldn’t mentally use a diet tracker like LoseIt on my unwanted days. The tracker decided that I should eat 1400 calories a day, so on fasting days it tells me that I am doing well, but also displays a warning that there is not enough food. Fair. But for the rest of the week, I’m tempted to stick to the 1400 goal, and the 5: 2 diet doesn’t work that way. I never feel ready for another day of fasting because I always felt a little hungry. So I ditched the tracker and easily returned to the 5: 2 rhythm.
MyFitnessPal can meet different calorie targets for each day if you pay for a premium subscription. I prefer to go without a tracker and let my calories drop anywhere.
Should I try?
This diet is definitely not for everyone. If you are comfortable with a plan that requires you to be undernourished every day, stick to that plan. You are not missing much.
But if you find it difficult to stick to a typical calorie-restricted diet, you may find intermittent fasting easier. The 5: 2 diet was designed as a form of fasting that is easy to follow: you get a little food, not all, and you can schedule your fasting days so that they always fall on those that work for you. You can even put them side by side if you like, but even Dr. Mosley admits that this is too difficult for most people.
The authors point out that there is nothing magic about 500 calories (men are even allowed 600 calories, or just 25 percent of what you usually eat). It’s the same with the schedule: they suggest that you cut to one day of fasting per week if you are maintaining your weight, or you can do three days of fasting if you are having fun and want to speed up your weight loss.
They offer another setting that I thought really helps: fasting for 24 hours instead of trying to survive a night, a full day, and then another night. This circuit is so simple that I found myself using it by accident. Have lunch late in the evening, say around 2:00 pm, and then skip dinner. When you wake up, if you can skip breakfast, all you have to do is postpone lunch again until 2:00 pm and bingo – you fast 24 hours a day.
I lost a few pounds by trying the 5: 2 diet, although I didn’t do it all the time, and around the same time I also changed some other things in my life, like exercising more. I’m not ready to give credit to the diet, but so far it suits me.
Whether this diet works for you will likely depend on how you spend your time (are you busy with your work schedule?), As well as how you deal with hunger and willpower. It’s definitely doable, and while trendy, it’s completely free of pseudoscientific claims. If you’re ready to give it a try, read the basic rules on the Fast Diet website and search the forums for advice, then pick a busy day and skip the kitchen.
This story was originally published 3/29/17 and updated 10/2/19 to provide more complete and up-to-date information.